1. Field of the Invention
The present invention relates to a substrate for a liquid discharge head for discharging liquid and a liquid discharge head.
2. Description of the Related Art
One of recording methods using inkjet heads typified by liquid discharge heads is a method in which bubbles are generated by heating ink with a heat-generating element and the ink is discharged using the bubbles.
Japanese Patent Laid-Open No. 2000-225708 discloses that a plasma SiN film formed by a chemical vapor deposition (CVD) process is used as a protective insulation layer for protecting a heat-generating element and wiring lines for driving the heat-generating element from ink.
An inkjet head in which the plasma SiN film disclosed in Japanese Patent Laid-Open No. 2000-225708 is used as a protective layer can be sufficiently protected from conventional ink. However, in recent years, various types of inks have been used for the purpose of enhancing ink properties such as color developability in printing by inkjet printers, weather resistance, and fixability to paper. Among these inks, there are some inks which dissolve protective layers, made of plasma SiN or plasma SiO, used for substrates for conventional inkjet heads.
In the case where a protective layer is dissolved in ink, a current may possibly flow into an energy-generating element generating energy for discharging the ink or a wiring line through the ink. This may possibly cause disconnection. Alternatively, the energy-generating element may possibly react with oxygen contained in the ink to cause disconnection. Therefore, there is a problem in that the reliably of an inkjet head is reduced by the dissolution of the protective layer.
Protective layers for substrates for inkjet heads need to meet performance requirements such as insolubility in ink, adhesion to a passage-forming member, electrical insulation, and processability.